During the past years, offshore drilling has continually increased. Given high costs and risks associated with offshore drilling, to avoid a dry well, marine seismic surveys are used to generate a profile (image) of the geophysical structure under the seafloor. While this profile does not necessarily provide an accurate location for the oil and gas, it suggests, to those trained in the field, the presence or absence of oil and/or gas.
A typical marine seismic surveying system is illustrated in FIG. 1. A vessel 100 tows a seismic source 102 and plural streamers 106, each streamer carrying an array of seismic receivers 104 (e.g., hydrophones). It is desirable to maintain the streamers at predetermined horizontal cross-line distances (i.e., along an axis perpendicular to the towing direction T), and at predetermined depths (e.g., 10 m) relative to the water surface 108. The seismic source 102 is configured to generate a seismic wave 110 that propagates downward (down, up and vertical being defined relative to gravity) toward the seafloor 120 and penetrates formations 125 under seafloor 120 until it is eventually reflected at discontinuity locations such as 122a and 122b . The reflected seismic waves 130a and 130b propagate upwardly and can be detected by one of receivers 104 on streamer 106. Based on the data collected by receivers 104, an image of the subsurface formation is generated by further analyses of the collected data.
To maintain the streamers at a desired position (i.e., such as to have predetermined cross-line distances and predetermined depths), conventionally, a head float 140 and a tail buoy 150 are attached to the ends of the streamer. Position control devices 160 (e.g., birds) may be attached to streamer, every 300 m, to control a position of the streamer.
Marine surveys often last for weeks or months, which is more than enough time for the survey cables to attract barnacles and other unwanted wildlife or debris. Such materials, when attached to the streamer, tend to increase drag on the cables, thereby requiring a greater amount of towing energy and placing increased strain on the ship, the cables, and the positioning devices. Such materials can also induce additional turbulence, which may impair the quality of the data acquired from the sensors distributed along the cable. Current methods of cleaning survey streamer cables tend to be time consuming, labor intensive, and generate premature worn to the streamer cables and its measuring instruments, as now discussed.
A conventional tool and method for cleaning survey cables is described in U.S. Patent Publication No. 2013/0098394 A1 (herein, '394 application), the entire content of which is incorporated herein by reference. The '394 application discloses, as illustrated in FIG. 2 (which corresponds to FIG. 3A in '394 application), a cleaning tool for cleaning a survey cable 202. This cleaning tool employs a cable guide 205 with a roller mechanism 206 that lifts the survey cable clear of the water and guides it through a scraper mechanism 211. As the cable guide 205 lifts and passes along underneath the survey cable, the cable exerts a frictional pull on the roller mechanism 206, causing it to turn at a rate that matches the speed of the cable relative to the workboat. The roller mechanism 206 is coupled via a belt drive system 204 to rotate a set of scraper wheels 210. The scraper wheels 210 have short bristles of plastic, wire, or some other material selected for its effectiveness at removing barnacles. These scraper wheels cause wear to the survey cable's surface due to their abrasive manner of removing the barnacles.
Due to the scraper wheels' abrasive approach in removing marine fouling, the streamer jacket becomes rough with the premature wear, which enables barnacles to settle more easily and at a quicker rate. This then creates an undesirable situation where the more one cleans the streamer, the faster the barnacles can return.
Further, due to the nature of the cleaning tool employed in FIG. 2, the belt drive system 204 is susceptible to erroneous behavior due to excess barnacle build-up. Any debris or marine contaminant that may enter inside the belt drive system, the roller mechanism 206, or the springs 216, used in this embodiment, would render the device inoperable.
There is, therefore, a need to develop non-destructive methods of cleaning to eliminate premature wear and mechanical parts that are prone to failure.